Modern disc drives are commonly used in a multitude of computer environments, ranging from super computers to notebook computers, to store large amounts of data in a form that is readily available to a user. Typically, a disc drive has one or more magnetic discs that are rotated by a spindle motor at a constant high speed. Each disc has a data storage surface divided into a series of generally concentric data tracks that are radially spaced across a band having an inner diameter and an outer diameter. The data is stored within the data tracks on the disc surfaces in the form of magnetic flux transitions. The flux transitions are induced by an array of read/write heads. Typically, each data track is divided into a number of data sectors where data is stored in fixed size data blocks.
The read/write head includes an interactive element such as a magnetic transducer. The interactive element senses the magnetic transitions on a selected data track to read the data stored on the track. Alternatively, the interactive element transmits an electrical signal that induces magnetic transitions on the selected data track to write data to the track.
Each of the read/write heads is mounted to a rotary actuator arm and is selectively positioned by the actuator arm over a pre-selected data track of the disc to either read data from or write data to the data track. The read/write head includes a slider assembly having an air bearing surface that, in response to air currents caused by rotation of the disc, causes the head to fly adjacent to the disc surface with a desired gap separating the read/write head and the corresponding disc.
Typically, multiple center-open discs and spacer rings are alternately stacked on a spindle motor hub. The hub, defining the core of the stack, serves to align the discs and spacer rings around a common axis. Collectively the discs, spacer rings and spindle motor hub define a disc pack assembly. The surfaces of the stacked discs are accessed by an actuator assembly which includes the read/write heads and the complementary stack of actuator arms. The actuator assembly also includes head wires which conduct electrical signals from the read/write heads to a flex circuit which, in turn, conducts the electrical signals to a flex circuit connector mounted to a disc drive base deck.
When the disc drive is not in use, the read/write heads are brought to rest in a landing zone which is separate from the data storage locations of the discs. The landing zone provides a non-data storage location on each of the disc surfaces where the read/write heads are positioned before the rotational velocity of the spinning discs decreases below a threshold velocity which sustains the air bearing. The landing zone is typically located near the inner diameter of the discs.
A continuing trend in the industry is the simultaneous reduction in size and increase in data storage capacity and processing speed of modern disc drives. As a result, the discs of modern disc drives increasingly have smaller diameters and tighter disc-to-disc spacings. Although providing increasing amounts of storage capacity, narrow vertical spacing of the discs gives rise to a problem of increased sensitivity to operational vibrations and to external mechanical shock. Additionally, as disc drives continue to decrease in size, smaller heads, thinner substrates, longer and thinner actuator arms and thinner gimbal assemblies continue to be incorporated into the disc drives. Faster seek times also demand increased velocity of the actuator assembly. These factors significantly increase the need to protect the disc drives from incidental contact between the actuator arm/gimbal assemblies and the disc surfaces.
The requirement for these non-data storage locations on the disc works counter to the general trend for ever increasing data storage capacity. As a result, it is necessary to limit the size of the non-data zones, and to precisely control the extent of actuator travel relative to the non-data zones. Otherwise, an actuator that travels beyond the desired extent of radial travel likely results in damage to the read/write head. The inner extent of radial travel allows the read/write head to travel inwardly past the inner most data track to the landing zone where the read/write head can be parked on the disc surface when the disc drive is non-operational. Inward travel beyond this inner extent of travel can result in damaging contact of the read/write head with the spindle motor hub. The outer extent of radial travel allows the read/write head to access the outer most data track. Outward travel beyond this outer extent of travel can result in the read/write moving beyond the outer edge of the data disc where there is no sustaining airflow, causing damage to the read/write heads which can contact one another or the spinning discs.
As requirements for faster data processing demand ever increasing actuator speed and associated deceleration rates during seek cycles, the likelihood of overshooting the target track increases. Such an overshoot near the extents of travel can resultingly damage the read/write heads. Also, unfortunately, control circuit errors are known to create "runaway" conditions of the actuator wherein the actuator fails to decelerate at the appointed time. To protect the read/write heads from catastrophic failure, it is well known and practiced in the art to employ positive stops which limit the actuator travel to locations only between the desired extents of travel.
In providing such a positive stop, or crash stop, it is necessary that the crash stop decelerate the actuator quickly and in a short distance, but without damaging the actuator assembly. The maximum deceleration is limited to that which is below the acceleration force limits of the actuator assembly, such as below the deceleration force that would cause the transducer to deflect away from a supporting member and thereby either contact the data storage surface or plastically deform the supporting member. As a result, numerous attempts to provide a controlled braking impulse to the actuator have been made.
Applying a general dampened braking impulse is known in the art, such as by the use of an air cylinder type dampener as taught by U.S. Pat. No. 4,937,692 issued to Okutsu. In this approach fluid is displaced by a piston that is responsive to a stop member that obstructs the movement of the actuator beyond the desired extent of travel. The dampened braking impulse provides a resistive force for decelerating the actuator, but without the typical sudden deceleration of a rigid stop member, such as a rigid stop pin.
Manufacturability and cost constraints have urged the art toward more simple mechanisms. The use of a resilient pad is widely known, such as that of the teaching of U.S. Pat. No. 4,890,176 issued to Casey et al. and assigned to the assignee of the present invention. Spring members, too, are widely used in the art, such as that according to the teaching of U.S. Pat. No. 4,635,151 issued to Hazebrouck.
The primary objection to resilient pads and springs is the relatively long stopping distances necessary to compress the responsive member sufficiently so as to develop an effective braking force. One attempted solution is to provide a preload force to the resilient member, such as is taught by U.S. Pat. No. 4,949,206 issued to Phillips et al. Another approach is to provide cantilever members that elastically deflect in response to the impact force of the actuator, such as is taught by U.S. Pat. No. 5,134,608 issued to Strickler and U.S. Pat. No. 5,600,516 issued to Phillips et al. and assigned to the assignee of the present invention.
Where the resilient member provides a superior initial impact response in not significantly increasing the peak deceleration rate, the relatively large amount of disc space necessarily reserved for stopping distance runs counter to the efforts in maximizing disc space utilization. The optimal solution for minimizing the stopping distance, as currently practiced in the art, is the use of a cantilevered stopping pin. Even so, the peak deceleration rates are difficult to control, and accordingly, there is a need for an improved crash stop apparatus for a disc drive that combines the control stopping distance performance of the cantilevered stop pin with the minimal peak deceleration performance of the resilient member.